48. Does homology infer design or common descent?

If you’d asked me ten years ago what homology was, I probably would’ve answered, “The study of… homos…?” I had no idea, because I’d never bothered to explore any evidence in favor of evolution. But it was evidence from homology — the study of similarities in animals due (allegedly) to common descent — that first prompted me to have second thoughts about evolution.

While Darwin may have been clued into evolution by birds, my personal journey began with man’s best friend: dogs. This was because, ironically, most creationists openly accept that all dog breeds originated from a single pair of dogs, and that this “kind” of dog was aboard Noah’s ark.

While you wouldn’t think creationists would be too eager to believe in such a rapid “micro-evolution” of dogs, this kind of variation is well documented, and it also helps to reduce the number of animals that would’ve been required to be aboard the ark, helping the ark story seem all the more plausible.

Even though today there are more than 350 variations of dogs, Noah only had to take one pair of dogs on the ark. Over time, during the 4,400 years since the flood, this one kind of dogs, through normal genetic variation, has given us the different varieties of dogs we see today. This isn’t evolution, it is normal genetic variation.
~Bob Knopf

Geneticists agree that all dogs descended from a single kind, and specify it was some type of wolf ancestor. All dog breeds carry the genes of their wolf ancestor, and even continue to exhibit a few wolf-like traits (e.g. howling). 

It was my curiosity about these rapid “genetic variations” that drove me to examine a few canine skulls, and I found the diversity among dogs to be quite extraordinary. It was amazing to think that from one type of dog, you could actually derive hundreds of very different skull shapes and sizes, and after just a few centuries of artificial selection.  

Pug skull (foreground) and gray wolf (background).

Pug skull (foreground) and gray wolf (background).

Granted, these dogs were still dogs, but their ability to change over time did suggest that our skeletons were highly malleable. I began to wonder… if a wolf can become a pug or a chihuahua after just a few thousand years, how much more might an animal change if given a few million?

A visit to the California Academy of Sciences

With these dog skulls on my mind, I paid a visit to the California Academy of Sciences in San Francisco, and it further changed the way I perceived evolution.

T-RexIt started with the T-rex skeleton. In my mind, humans had absolutely nothing in common with tyrannosaurs. And yet… I couldn’t deny the existence of similarities in our body plans: we both had vertebrae and a rib cage, arms, legs, knees, shoulder blades, hands, feet, and a skull with two eyes, a nose and mouth all arranged in the same general order.

Next came the museum’s blue whale. Again, its skeleton was also different from our own, but it too had ribs, a spine, and… arms. Arms? What was a whale doing with arms? I’m embarrassed to admit that I’d never really noticed how similar a whale’s arms are to our own… the fingers, the wrist bones, the radius and ulna, the humerus… even the shoulder blades were located in the same position.


Again I wondered… why would God create flippers out of arms and hands if he didn’t have to? It seemed like an odd choice. It was as if God had already testified by every fish in the sea that fish-like pectoral fins were the de facto standard for ocean dwellers, yet when it came to the whale, he decided, “Eh, I guess arms could work too.”

Later that day I perused their display of human skulls. As any good creationist knows, there are no “transitional” forms, there are only apes and humans with minor variations within each kind. But clearly, these skulls suggested that we humans could also undergo changes to our skulls, just as the dogs had done. 

SF Skulls

Lastly, I came across something I found even more compelling: the skeleton of a ring-tailed lemur.

LemurOn the outside, lemurs look very little like us, but under the skin, they are surprisingly similar. The arms, the legs, the shoulder blades, the pelvis, the ribs, and especially the tiny hands and feet… it’s all there, just shaped slightly different. Admittedly the skull was pretty different, but from what I’d seen in dogs and humans, I knew that skull shapes could change dramatically.

Upon returning home, I pondered these similarities, and began looking at pictures of other primate skeletons. There were some, like the spider monkey (below), that already had a skull that was much more human-esque than the lemur’s. In fact, just drop the tail and stand the spider monkey upright, and it appears almost human.


I wondered more… if dog skulls can change so drastically, and monkey and human skeletons were already similar, how can I argue that it would be impossible for (at the very least) the skeletal system of a primate to take on the shape of a human? This wouldn’t make it human, but it would have a nearly identical infrastructure. Just upgrade the brain, and you’re pretty much there. 


Tetrapod Limbs

Since then, I’ve learned what I’d inadvertently “discovered” was a branch of evidence for evolution known as homology. The great thing about homology is that you don’t need to be an expert in comparative anatomy to see these similarities. You can look at the forelimb of a human, a lizard, a cat, a whale, a bat, a frog, or a bird and see the same bones performing different functions.

Human vs. Dog skeleton

And it doesn’t end with forelimbs, you can take any two mammals or reptiles and find equivalent structures throughout each.

Forelimbs of people, porpoises, bats and horses provide the classic example of homology in most textbooks. They look different, and do different things, but are built of the same bones. No engineer, starting from scratch each time, would have built such disparate structures from the same parts.
~ Stephen J. Gould, The Panda’s Thumb: More Reflections in Natural History, 1980

Creationist explanations for homologous relationships

So why do different species share such striking similarities? According to biologist and creationist Jerry Bergman, God created “systems” of animals, like mammals and reptiles, and then modified them so they could survive on land, in the air, and in the sea:

The many similarities that exist among members of the animal kingdom is the result of the fact that a single designer created the basic kinds of living ‘systems’, then specially modified each type of life to enable it to survive in its unique environmental niche. Examples of major environments for which organisms must be designed include the air, ground and water.
Jerry Bergman, Ph.D., Biology

Assuming this is true, it’s curious that God should equip some animals for one niche, and then place them in another. Why equip flightless birds with wings for the air niche, but then place them in the ground niche? Or why modify mammals and reptiles (e.g. whales, dolphins, manatees, sea turtles, etc.) to live in the water niche, but then equip them with the lungs of an animal intended for the ground niche? With evolution we expect such nonsense, but with a designer?

Also, if God did adapt these animals to survive in these niches, why then have so many  failed to survive in the niches God prepared them for? Did God design them to go extinct? Was he unaware of the environmental changes they would surely face?

And finally, a full transition from sea-to-land and back again is time-consuming. If evolution did occur, we should expect to find very few mammals and reptiles occupying the open ocean compared to all other types of marine life, and this is the kind of thing we observe. It would’ve been no trouble for God to populate our oceans with mammals or reptiles, but he didn’t, once again making his creation frustratingly consistent with evolution.

Transitional forms

While evolutionists focus on similarities, creationists focus on differences, often claiming that some of these differences are impossible to explain via evolution.

Even similarities among somewhat similar creatures reveal that the differences are more important than the similarities.
Answers in Genesis, March 1, 1992

Creationists add that no fossils exist that show a transition from any one kind of animal to another. Evolutionists object, and point to fossils like Tiktaalik (fish to land animal), Tritheledontidae (reptile to mammal), Archaeopteryx (dinosaur to bird), Ambulocetus (land mammal to whale), Darwinius masillae (prosimian and simian), Australopithecus (ape-like ancestors to human), and so on, but creationists counter by saying that because no one observed these transitions, God may have created them in the form they were all found in.

Homologous vs. Analogous similarities

Marsupial Tasmanian Wolf

I should also note that not all homologous similarities stem from common decent. For example, marsupial moles, wolves, and anteaters resemble their unrelated placental equivalents, but did not descend from them.

Creationists say these similarities exist because God (who must’ve been running out of ideas) remade similar animals in different classes. Evolutionists say these analogous similarities are the result of convergent evolution, and that these animals developed similar features because it helped them to accomplish similar tasks (e.g. long noses are beneficial to all ant eaters).

Barbara ManateeAn interesting example of homology vs. analogy can be seen in whales, dolphins, and manatees. Whales and dolphins share homologous similarities with each other, but analogous similarities with manatees.

The distinctive homologous traits that suggest whales and dolphins had a common ancestor include the shape of their flukes, the bones in their flippers, and their trademark blowholes. Meanwhile, the manatee is also believed to have returned to the sea (or was modified for the sea), but seems to share only analogous similarities with whales and dolphins.

All three have traded in their hind legs for flukes, but the manatee’s fluke has a distinctively different shape. All three have also traded in arms for flippers, but the bones in the manatee’s flippers remain much more hand-like in appearance. And while whales and dolphins share the same tell-tale blowhole, the manatee has retained his nose.

Whale, dolphin and manatee fin/flipper.

Whale, dolphin and manatee fin/flipper.

Was the blowhole not good enough for God to reuse on the humble manatee? If God is modifying mammals for the water niche, why not equip them with the same equipment? If he’s not going to give the manatee gills, the least he could do is give him a blowhole.


In the same way I can see the familial relationships in dogs, I look at the blowholes on whales and dolphins and see a familial relationship. Likewise, I can look at the trademark pouches on all the marsupials stranded on Australia and infer that they too must all be related. And if all of those animals are related, it’s not too difficult to look at the similar skeletal structures of monkeys, apes, and humans and infer a similar familial relationship.

If evolution did occur, we would reasonably expect to see these kinds of relationships, and we do! Homology by descent is not only consistent with the evolutionary model, it is also easily falsifiable: if all animals are not homogeneously related, then evolution is patently false! But they are. 

But is homology also consistent with a designer? We can never be sure, because no one knows if a designer would need (or want) to design homologously. And unfortunately, we cannot falsify homology by design, because no matter how similar or dissimilar two animals may be, or how oddly designed, or how many may go extinct, the creationist can always claim that this is the way God wanted it.

In the end, I think evolution does gain some credibility from homology (alone) simply because it’s consistent with what we’d expect to see if evolution were true. God was certainly under no obligation to design every single animal homologously (especially those created in his image), and it might even be considered somewhat deceptive for him to have done so. Homology by descent can also be falsified, while the nature of homology by design does not allow for potential falsification or even criticism (beyond citing a few seemingly inept designs).

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18 Responses to 48. Does homology infer design or common descent?

  1. refinedrandomness says:

    Hi there, like your blog very much. Appreciate your philosophies…and the last paragraph sums it up ….. excellent, enjoyed this.

  2. Alpha says:

    Job well done, 500Q! I admit I did get worried when you disappeared for a while, but no matter😀 A point to add: I never debate creationists. And this is because most creationists have already rejected the idea of evolution before the conversation has started – WITHOUT bothering to research what evolution is actually about. This just creates a one-sided conversation where the only answer I can give to any of their questions is “not applicable. Please do your research before you argue your point, because that is NOT what evolution is.” It’s actually quite frustrating.

    I found this video completely by accident

    I think, seriously, this is SO close to child abuse. I’d like to hear your thoughts on it guys!

    • Thanks, I’m glad someone noticed.🙂

      I’ve been busy vacationing with the family this summer, and reading about homolgy (and other things). But still have lots of other questions.

      “It just makes more sense to me!”

      This is what really amazes me. This woman is essentially saying, “I require ABSOLUTE PROOF of evolution before I’ll believe it, but I’m willing to accept everything in the Bible on faith.”

      Why is proof required for evolution, while no evidence is required for: belief in talking snakes and donkeys, the existence of angels and demons, eternal and invisible spirit beings, parting seas, calling fire from heaven, global floods, Noah’s ark, Jonah and the whale, ordering the sun and moon to stand still, the virgin birth, the trinity, the resurrection, and so on? Almost every geologist, archaeologist, and paleontologist on the planet would say “There was no global flood,” but screw them, I’ll just take it on faith that the Bible is right and these experts are misreading the evidence (as if they’ve never heard these arguments from the Bible).

      But I have to admit, 10 years ago I would’ve seen nothing wrong with this kind of teaching. What can I say? I was ignorant and afraid.

      But in their defense, the evidence for evolution isn’t easily apparent; it doesn’t get in your face and say, “Believe in evolution or you will burn in eternal hellfire!” It’s not as obvious, you have to be willing to take the time to understand it.

      • Alpha says:

        Good point there. Religion says, “It happened! And it makes a lot of sense. and if it doesn’t, hey, that’s ok too because God is a million times smarter than you are.” Whereas evolution has a lot of explanation and science behind it you need to understand, which is why they don’t teach it until you’re much older. It’s unfair to the children, to tell them this stuff before they can decide for themselves. But it is true: believing in something bigger than yourself is a lot easier, it takes huge responsibility off your shoulders.

      • Anonymous says:

        I notice. I have this site bookmarked and check it every week or so. I get excited every time you post a new update. Keep up the good work.

      • Alpha says:

        Something I just realised… does the Bible actually say that dinosaurs existed a few thousand years ago? I have never heard a Christian argue that with anyone, ever. Dinosaurs just get avoided, stat. Or else it’s a half-hearted explanation that’s just thought up on the spot.

        And “authority of scripture”. Ah. Now that, that’s interesting. The way Christians view it, the Bible was God breathed. But then it’s also interesting to consider that the Bible was written by humans, not by God.

        “The Bible did not arrive by fax from heaven… the Bible is the product of man, my dear, not of God. The Bible did not fall magically from the clouds. Man created it as a historical record of tumultuous times, and it has evolved through countless translations, additions and revisions. History has never had a definitive version of the books.” — Dan Brown, The Da Vinci Code.

        And it’s true. The Bible was written by humans. The Quran and the Tao were written by humans. Harry Potter and Twilight were written by humans. So… um… of all books, the Bible was inspired by God, and we can tell… because… um… isn’t it obvious?? And there it goes. Christians don’t need hard evidence that the Bible was inspired by God. They just believe it. But they will never ‘just believe’ in evolution. (nor should they, because it’s science and science encourages understanding, not blind belief. But either way it shows the contradictory nature).

        • Re: Dinosaurs: What the Bible does say is that all animals were created during the 6 days of creation (at the same time). The Behemoth and Leviathan in the book of Job (40 and 41) are sometimes cited as examples of eyewitness descriptions of dinosaurs.

          But there are a large number of problems with this theory. For example, we never find dinosaurs buried with a mix of ancient and modern animal fossils. And we’ve never been able to extract DNA from dinosaurs, because they’ve been extinct for too long (DNA degrades after about 100,000 years). We can still get DNA from more recently extinct animals like mammoths and saber tooth tigers, but not dinosaurs.

          Job appears to be speaking of mythological monsters that can do things like “breathe smoke from their nostrils” (41:20). Although… even if we discovered a dinosaur today it wouldn’t prove it was created alongside all the other animals, it only proves it didn’t go extinct (like a number of ancient animals that still exist today).

          Re: The inspiration of the Bible, that’s another interesting question. How do you PROVE the Bible is inspired by God? For me personally, it came down to miracles, prophecy, and my personal feelings about God (and some other evidences). But the closer I look at these things, the more I find the evidence is pretty thin. I think we all just want an explanation for things, and Christianity provides one (and a lot of other things).

          If the Bible WERE truly inspired by God, there are a great many other things God could’ve said or done to establish himself as the author, such as describing DNA, or the solar system, or the microscopic causes of disease. Instead, we have miracles that must also be believed on faith (because they left little or no evidence), and ambiguous and controversial prophecies. Heck, even the Jews (of all people) didn’t see Jesus as fitting their prophecies. I think this shows just how controversial these prophecies were — even the people who believe in the Bible can’t all agree on what they are predicting.

          • Alpha says:

            Common descent is really not all that hard to see, if you simply observe some things which are there for you to see. The hardest part is probably starting to see these things in the first place; but once you do, you practically start finding them everywhere.

            Of course, dogs are one of the most common examples and probably also the easiest to see. All dogs are descended from the single species of wolf – the grey wolf. There’s a whopping variety of different dogs from the Chihuahua to the Great Dane, And since most of the many dog species were a result of selective breeding, over a relatively short period of time, is it really that hard to believe that, over *millions* of years, a new species evolved? I couldn’t agree more with your point there, 500Q =)

            Just as an added thought: what exactly does Knopf mean by “normal genetic variation”? Genetic variation is essentially the entire baseline of evolution; without genetic variation, there is no evolution, and with genetic variation, there would obviously be changes occurring in the species. Explaining the existence of more than 350 different species of dogs by “genetic variation” is basically supporting the basic idea of evolution… isn’t it? O.o

            • Most creationists, like Knopf, accept that genetic variation exists, but they believe that God has imposed natural limits to this “micro-evolution” that prevent one species (or kind) from ever becoming another. But I agree with you, it doesn’t take a big leap in reasoning to see that this is exactly what has happened, especially when you look at animals like whales and dolphins, or the marsupials stranded on Australia — clearly one has come from the other.

    • Daniela says:

      How do you consider this as child abuse? Can you elaborate more on your thought?

      • David says:

        The brainwashing of children is clearly child abuse. Children deserve a proper education; an education that doesn’t include that kind of clap trap. It can take a lifetime to recover from religious indoctrination.

        • Amen to that, I’m still trying to recover from my indoctrination. Kids should be free to grow up without religious indoctrination, and left to decided what they want to believe when they’re older.

    • Simon Pete says:

      I agree this is close to child abuse. I am just recently become an atheist. Still totally in the closet. On this subject “Give me 100% proof of evolution and I will believe it, yet I believe creation without any proof” nonsense. When I was a young teen and a born again on fire Christian I went to a youth conference and the speaker was a total holy roller on fire for the Lord 100% bible is true type of guy, and he told us that the bible was the ultimate truth, he would even believe it 100% if it said Jonah had swallowed the whale.

    • M Rae says:

      Thank you for posting the video. I am in the process of learning the truth, much like 500q. I have a daughter and struggle what to do. She gets a lot of great things from church such as friends and a sense of belonging. Yet in my heart I feel like what she is being taught is so wrong and the longer I let it go on the more indoctrinated she will become.

  3. rautakyy says:

    Good to have you back!

    If there is a designer, why would that designer go to such lengths, to conceal the design? Why make it look like there is no design, but that the variety of life emerged naturally? And if there is a designer, how can we infer who that designer was and what was the intent of the design? Even if we had a revelation from such a designer, in which that entity told us what the purpose was, then would it not be natural conclusion, that this entity is not a reliable source for what this entity is all about?

    And further more, if the revelation from the assumed designer of the nature who could offer all of us this revelation, was only offered to a limited group of people living in primitive culture and therefore unable to evaluate this kind of information as the homology, would it not be natural conclusion, that these alledged revelations are not indistinguishable from mental disorders?

  4. Dovregubben says:

    I think your Stephen Jay Gould quote should contain the word disparate, not desperate.

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